Biomass, and in particular sugars therein, are considered an important and sustainable source for building blocks previously made from petrochemical sources. Interest in mono-, di- and polysaccharides is increasing. The resulting 5-HMF may be used as fuel or fuel additive, but also as precursor for a building block in polymers (e.g. polyesters) and the like. For instance, Avantium is currently developing a process for the production of polyethylenefurandicarboxylate (PEF) from C6 sugars as a next generation replacement material for polyethyleneterephthalate (PET).
The conversion of in particular glucose and fructose has been studied in detail. For instance, it is known that fructose is more efficiently converted to 5-HMF than glucose. The conversion is typically conducted with an acidic catalyst, a homogeneous or a heterogeneous catalyst, more preferably a solid catalyst. Also, various solvent systems have been used, e.g., organic solvents, ionic liquids, etc.
Methods for the manufacture of 5-hydroxymethylfurfural and ethers thereof are described in for instance EP2103606 and EP2565189. The hexose-containing starting material is typically fructose or glucose.
More recently saccharides (sugars) other than fructose and glucose have been studied. The reason for this lack of interest in the past is that one would expect no significant differences in reactivity and selectivity between the various saccharides.
In Energy Environ. Sci., 2010, 3, 765-771, “Mechanistic insights on the conversion of sugars into 5-hydroxymethylfurfural”, a paper by Binder et al, the transformation of D-mannose and D-galactose into HMF was studied. Also studied was the transformation of lactose and D-tagatose. The reactions were conducted in an ionic liquid, dimethylacetamide (DMA) or dimethyl sulphoxide (DMSO). The investigation revealed that some, but not all hexoses, can be transformed efficiently into HMF. Among others D-psicose, D-tagatose and L-sorbose were studied. In one experiment the yield of HMF from psicose with H2SO4 in DMSO was higher than the corresponding conversion of sorbose. In many other experiments the yields of HMF from psicose and sorbose were similar. Other experiments provided proof of poor reactivity of tagatose.
The article states that the HMF yield of HMF from psicose with H2SO4 in DMSO is similar to those obtained with fructose. It concludes that among fructose and its three epimers the highest HMF yields were obtained from fructose and psicose.
In a paper submitted to ChemSusChem, 2013, 6, 1681-1687, “Dehydration of different ketoses and aldoses to 5-hydroxymethylfurfural”, by Van Putten et al, a kinetic study on the acid-catalysed dehydration of ketoses and aldoses was reported. Acid-catalyzed dehydration in water with different concentrations of sulphuric acid at various reaction times revealed tagatose to be the more reactive saccharide as compared to sorbose and fructose. Modelling studies indicated that psicose, which was not tested experimentally, would be the least reactive ketose for the dehydration towards HMF.
EP 1834950 discloses a method for the manufacture of ethers of 5-hydroxymethyl furfural by reacting a glucose-containing starting material with an alcohol in the presence of a catalytic or sub-stoichiometric amount of acid catalyst. The process can also be applied to sucrose and be performed in a continuous flow reactor. The patent application does not mention the use of any starting material other than glucose or fructose.
The inventors set out to find monosaccharides that can be converted into 5-HMF in water or the ether derivative thereof in an alcohol, that are better than fructose. This has now been achieved.